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Full text of "Text Book Of Mechanical Engineering"

74

Blast-furnace Action.

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formed by the combination of the flux with the impurities of the
ore, is separately withdrawn.    (See Appendix //., p. 788-9.)

The action in the blast-furnace is this :—Air being introduced
by the blast to give us oxygen, and coke to provide carbon; then,
if the coke be heated to redness, carbon dioxide is formed,

From
Air.     Coke.

20      +      C        :

Gas.
C02

As this gas ascends it takes up carbon from the coke, which it
passes on its way, thus :

Carbon                  Carbon

diox.      Coke.     monox,

C02 + C =  2CO

And we now have carbon monoxide.

Ascending further, this last-mentioned gas meets the iron ore,
which is now at a great heat. The oxygen in the ore has then
the choice of remaining where it is (Fe208) or of combining with
the C 0 \ preferring the C 0, it forms with it carbon dioxide once

more,

Carbon                             Carbon

monox.          Ore.              diox.          Iron.

3CO

2Fe

And the iron is now left, but in a viscous condition. As it takes
up carbon, however, it becomes more fluid, descends to the
bottom of the furnace, and may be then run out

Other substances have also been absorbed, which may be seen
on reference to the table at the commencement of Chapter I.,
shewing the general composition of the different pigs — grey,
mottled, and white.

Sulphur produces red-shortness in cast iron, that is, makes it
brittle when red hot, and Silicon and Phosphorus cold-shortness,
or brittleness when cold.

Carbon increases fluidity at the expense of strength, and
Manganese seems to have the effect during the smelting of in-
ducing the combination of the carbon with the iron, thus tending
to prevent the formation of graphite.

(2.) Wrought Iron. — The white pigs are broken up and
subjected to the processes of refining 2ci\& puddling. As, however,